The invention relates to locks, and more particularly to high security locks for sliding doors.
In existing sliding doors, such as glass patio doors, the door is locked from the inside by a simple hook mounted in the leading edge of the door and which is pivoted by means of a handle to engage the strike plate in the door frame. It is generally not possible to lock or unlock the door from the outside and accordingly the sliding door cannot safely be used as an exit when the house is being left unattended for an extended period, nor can entry to the locked house be made by the home owner through the sliding doors. Further, the latch cannot generally be locked in place using a key. Another common drawback with existing sliding doors is that once a burglar has gained entry to the house he can exit through the sliding door without difficulty.
Various locking devices have been developed to allow sliding doors to be locked as the party exits. For example, U.S. Pat. No. 2,666,319 issued Jan. 19, 1954 to Price discloses a combined latch and lock for sliding doors which is key controlled from the outer side of the door and finger controlled from the inside of the door. One limitation of the design of this lock is that it does not provide a means for preventing from the inside the opening of the door by a key from the outside. Further, this lock is relatively easy to pick, and access can easily be gained from the outside by breaking the glass in the vicinity of the lock and reaching in to operate the inside handle.
Similarly, U.S. Pat. No. 3,177,687 issued Apr. 13, 1965 to Tucker discloses a lock and latch mechanism for sliding doors. Here the latch is operated by both a handle from the inside of the door and a cylinder lock mechanism from the outside of the door. Again, there is no way from the inside to prevent the opening of the lock by a key from the outside, nor to prevent the unauthorized rotation of the interior handle and the lock is thus less secure from unauthorized entry.
U.S. Pat. No. 3,216,229 issued Nov. 9, 1965 to Moncada discloses a door latch device which may be latched or unlatched from inside the door by means of a manually rotatable knob. The latch may be unlatched from the outside by a key operated member engaging the rotatable knob. A slidable knob is provided which prevents the latch from being unlatched from the outside. In this design the tongue assembly is mounted in the door frame. One of the limitations of this device is that it does not permit positive locking of the latch with a key from the inside. Thus, an intruder could break the glass and insert a hand or wire to open the door and gain entry.
U.S. pat. No. 3,390,557 issued July 2, 1968 to Erickson et al. discloses a latch which may be opened from the outside by a key and from the inside by a manual member. A safety latch is disposed inside and, when in the active position, prevents unlocking by the key. The latch is also designed to prevent unauthorized opening of the door from the outside by a knife blade or similar tool. Again, however, positive locking from the inside using a key is not possible, and an intruder could simply break the glass and open the latch from the interior.
U.S. Pat. No. 4,378,684 issued Apr. 5, 1983 to Dugan et al. discloses a locking mechanism for a sliding door in which exit through the door can be positively prevented. Locking cylinders on either side of the door operate directly on an arcuate latching device. However, unlatching of the door by the external key cannot be positively prevented. An intruder could gain entry by picking or breaking the exterior lock.
U.S. Pat. No. 4,563,885 issued Jan. 14, 1986 to Madden et al. discloses a lock assembly for sliding doors in which the operation of the latch from the inside or outside can be prevented by the operation of a key from the outside. Thus picking or breaking the outside lock allows access and the door cannot be locked from the inside.
All of the above prior art locks are "mortised" locks in that they require mounting within the door itself, as opposed to rim locks which are mounted on the side of the door, such as that shown in U.S. Pat. No. 3,596,954 issued Aug. 3, 1971 to Hull et al.
Thus, none of the prior art locks for sliding doors provide a lock which can be positively locked from both outside and inside the door using a key, allowing the home owner to use the sliding door as an exit door yet allowing security from unauthorized entry.